1) Field of the Invention
The present invention relates to a powdered crosslinkable textile binder composition and also to processes for producing polymer bound textile moldings or sheet materials using the textile binder composition.
2) Background Art
Textile sheet materials produced by the customary methods for producing nonwovens, for example by the airlay, wetlay or spunlay process, require a binder for durable binding of the fibers and for increasing the resistance to mechanical stress. These binders are customarily based on synthetic macromolecular compounds and, in the prior art, can be applied either in the form of solids, for example as powder, granulate or fiber, or in the form of liquids, for example as aqueous polymer dispersion or solution. The increased strength of the nonwovens is due to the bonding of the fibers by the polymers which adhere to the fiber and so reinforce the fibrous structure.
WO-A 90/14457 discloses a process wherein carded glass fibers are mixed with thermoplastic powder, for example polypropylene, polyester or polyamide, and the fibrous structure is subsequently consolidated at elevated temperature and under pressure. AU-B 36659/89 likewise describes a process for consolidating glass fiber materials by means of thermoplastic powders. The use of powders based on polyester or polystyrene is recommended. The low strength of the thus-bonded fibrous structures on contact with water or solvents is disadvantageous.
Since the glass transition temperatures or the melting temperatures of the binders are frequently exceeded at elevated temperatures, durable chemical crosslinking of the binders is required in order that a high temperature dimensional stability is given to the fibrous structures. Processes are known for consolidating fiber materials composed of polyester, polyamide or cotton fibers using self-crosslinking polymer dispersions (U.S. Pat. No. 4,451,315). True, nonwovens of high strength are obtained, but the use of aqueous binders is prohibitively costly on the drying side. In addition, it is not a straightforward matter to disperse the binder in the fiber matrix.
U.S. Pat. No. 4,612,224 describes the consolidation of powdered crosslinkable copolymers based on phenol-formaldehyde resins. The disadvantage with this binder system is the high amount of formaldehyde emitted in the course of the production and use of the fiber materials thus consolidated.
WO-A 94/20661 describes self-crosslinking redispersible dispersion powders based on vinyl ester copolymers or (meth)acrylic ester copolymers as fiber bonding agents. The disadvantage with this binder system is that setting requires an appreciable input of water into the fiber matrix, entailing costly drying.
U.S. Pat. No. 4,129,545 describes thermosetting copolymers based on acrylic esters and/or vinyl esters and additionally containing (meth)acrylic esters of mono- or polyfunctional hydroxycarboxylic acids and N-alkoxyalkyl(meth)acrylamide as crosslinking component for use as a powder paint. EP-A 721004 discloses crosslinkable water-dispersible powders including both filming polymers having at least one functional group and reactive components which form covalent bonds on dispersion of the powders in water. Aqueous dispersions of the powder composition are used for producing water resistant coatings.